The present invention relates to a discharge lamp lighting device, or a starter of a fluorescent lamp with a semiconductor element.
FIG. 1 is a prior fluorescent lamp starter circuit which has a non-linear dielectric element and a semiconductor switch like a thyristor. In FIG. 1, the reference numeral 1 is a fluorescent lamp, 2 is an inductive balast, 3 is a semiconductor switch, 4 is a non-linear dielectric element, 5 is a capacitor for noise prevention purpose, and U and V are power supply terminals.
The fluorescent lamp 1 has filaments 101a and 101b at both the extreme ends of the same. The semiconductor switch 3 has a thyristor 301, a trigger element 302 (SBS(Silicon Bilateral Switch), or a diac), resistors 303a and 303b, and a capacitor 304.
When an alternate voltage e.sub.uv as shown by the dotted line in FIG. 2 is applied to the power input terminals U and V, the thyristor 301 turns ON at the phase .theta..sub.1 in the positive half cycle, then, the thyristor 301 closes and the current flows from the terminal U, through the balast 2, filament 101a, thyristor 301, filament 101b, to the other terminal V. Thus, the filaments 101a and 101b are pre-heated. Next, at the phase .theta..sub.2 in the negative half cycle, when the current in the thyristor 301 becomes zero, that thyristor 301 turns OFF. At that time, the voltage across the non-linear dielectric element 4 is zero, and the power supply voltage e.sub.uv is close to the peak voltage in the negative polarity, therefore, the non-linear dielectric element 4 is charged as shown in FIG. 2 through the balast 2.
The non-linear dielectric element 4 has the saturable characteristics between the applied field V and the charge Q as shown in FIG. 3, and has the non-linear nature, in particular when the applied field V exceeds the saturation voltage E.sub.s. Therefore, if the saturation voltage E.sub.s is lower than the peak voltage of the power supply voltage, the current flowing into the non-linear dielectric element 4 decreases suddenly when the instantaneous voltage of the power supply exceeds the saturation voltage E.sub.s. When the current decreases suddenly, the pulsive spike voltage V.sub.21 which is extremely higher than the peak value of the power supply voltage is induced across the inductive balast, and that voltage V.sub.21 is applied across the fluorescent lamp 1. The value of that spike voltage V.sub.21 depends upon the differential current (di/dt) and the inductance L of the balast 2. After that spike pulse V.sub.21 disappears, the power supply voltage e.sub.uv is applied to the fluorescent lamp until the thyristor 301 turn ON again.
The above operation continues until the fluorescent lamp 1 is fired. When the filaments 101a and 101b of the fluorescent lamp are pre-heated sufficiently, the fluorescent lamp 1 is fired by that spike voltage V.sub.21, and/or the positive voltage V.sub.11 by the spike voltage before the time O.sub.7. When the fluorescent lamp 1 is fired, the voltage across the lamp decreases because of the presence of the balast 2, therefore, the thyristor 301 does not turn ON during the fired period of the fluorescent lamp 1.
It should be noted that the voltage across the fluorescent lamp 1 becomes higher than the power supply voltage, as shown by V.sub.12 and V.sub.22 in FIG. 2, due to the charging operation of the non-linear dielectric element 4. Those high components V.sub.12 and V.sub.22 are absorbed by the capacitor 304, and therefore, the thyristor 301 does not turn ON by that voltage V.sub.22.
The circuit of FIG. 1 fires a fluorescent lamp with a non-contact switch and a non-linear dielectric element, and has the advantage of the quick start of a lamp. The firing time with the circuit of FIG. 1 is less than 0.8 second, which is extremely shorter than that of a prior glow-lamp type starter. It should be noted that it takes 2-8 seconds in a prior glow-lamp type starter. Further, the circuit of FIG. 1 has the advantage that the device is light in weight, and small in size as compared with a prior rapid-starter type circuit.
However, the circuit of FIG. 1 has the disadvantage as described below. Supposing that a power switch is switched on at the phase .theta..sub.0 in FIG. 2, then, the filaments 101a and 101b are heated during .theta..sub.1 and .theta..sub.2, but the pre-heating in that period is not enough, and the temperature of the filaments is insufficient to fire the lamp. By the way, at the phase .theta..sub.4, the high spike voltage V.sub.21 is induced, and is applied to the filaments, which are not heated enough. It should be appreciated that the radiation material, like Barium-Oxide (BaO), attached on the surface of a filament for radiating hot electron is sputtered and deteriorated when high voltage is applied to that radiation material which is not hot enough. The amount of the sputtered material is significant since the spike voltage V.sub.21 is applied for each cycle of the power supply voltage until the fluorescent lamp is fired. Thus, a prior circuit of FIG. 1 has the disadvantage that the life time of a lamp is rather short.